Radiation is a form of energy in motion through space. It is emitted by one object and absorbed by another. Particular radiations are examples for these radiations and they have mass and charge except neutrons which are neutral particles. The velocity of their motion depends on their kinetic energy. The particulate radiations originate from radioactive decay, cosmic rays, nuclear reactions and so forth.
The radioactive decay is a random process, and it is not possible to tell which atom from a group of atoms disintegrates at a specific time. Thus, one can only talk about the average number of radionuclides disintegrating during a period of time.
The radioactive elements undergoing a spontaneous transformation. The transformation theory did not stipulate a particular cause inside the atom, which would be responsible for the emission of alpha particles at a particular time and thus bring about a chemical change.